1. Field of the Invention
The present invention concerns a switching matrix of the type having a first number of inputs and a second number of outputs with a conductor arrangement and controllable switching elements by means of which the inputs can be selectively connected with the outputs.
2. Description of the Prior Art
In the transmission of electrical signals, it is frequently necessary to route a number of input signals. For example, a switching matrix is necessary to route magnetic resonance signals acquired by a number of local coils to corresponding receivers. In general, all local coils are not always simultaneously located in a homogeneity volume of the magnetic resonance apparatus and thus each coil does not always receive a magnetic resonance signal. Furthermore, the number of local coils frequently exceeds the available analog/digital converters that convert the signal for further processing. It is therefore necessary to use a switching matrix so that the local coils can be variably connected with the analog/digital converters. For example, there are magnetic resonance apparatuses with 32 acquisition channels to which analog/digital converters are connected. If 64 local coils for examination of a patient are positioned in an examination, the local coils are variably connected with the 32 analog/digital converters by the switching matrix.
The switching matrix can be realized as a distributor network that is composed of conductors that lead from the local coils to the acquisition channels and are arranged in rows and columns. At each intersection point of the various lines, a controllable switch is present that can connect or separate the corresponding intersecting lines and thus connect the respective local coil with the respective analog/digital converter. In the example of 64 local coils and 32 acquisition channels, 2,048 controllable switching elements are necessary. One possibility for the realization of such a switching matrix is the use of semiconductor technology. Each switch can be formed by semiconductor components, with one to three semiconductor components being necessary for each switch. Capacitors and coils are still additionally used to separate the control signal of the switch from the radio-frequency voltage to be switched. In total, more than 10,000 individual semiconductor elements are required to realize such a switching matrix. It is additionally necessary to activate each switch in the switching element by means of a separate control line via which the control signal is supplied. A control unit is necessary for each control line for generation of the control signals. Such a high number of control units can not be realized on one chip even in customer-specific integrated circuits.
A further possibility for the realization of controllable switches is micro-electromechanical components (MEM). In particular electromechanical relays or switches are of interest for the application in the switching matrix. Because such switches close the conductors via a mechanical contact, they exhibit a good linearity in terms of their analog signal transfer performance. The use of such components, however, also requires a separate control line and a control unit.